标签：sig 数值 roo 空格 strong ica 多选 指定 def
数据类型
mysql 常用数据类型
#1. 数字：
整型：tinyint int bigint
小数：
float ：在位数比较短的情况下不精准
double ：在位数比较长的情况下不精准
0.000001230123123123
存成：0.000001230000
decimal：（如果用小数，则用推荐使用decimal）
精准
内部原理是以字符串形式去存
#2. 字符串：
char（10）：简单粗暴，浪费空间，存取速度快
root存成root000000
varchar：精准，节省空间，存取速度慢
sql优化：创建表时，定长的类型往前放，变长的往后放
比如性别 比如地址或描述信息
>255个字符，超了就把文件路径存放到数据库中。
比如图片，视频等找一个文件服务器，数据库中只存路径或url。
#3. 时间类型：
最常用：datetime
#4. 枚举类型与集合类型
enum 和set
1. 数值类型 & 浮点型 & 日期类型
1.1 数值类型
整数类型：TINYINT SMALLINT MEDIUMINT INT BIGINT
作用：存储年龄，等级，id，各种号码等
数据类型 无符号(unsigned)和有符号 用0填充 zerofill
约束的作用: 保证数据的完整性和一直性
tinyint [-128~127] 小整数
int 整数
bigint 极大整数
create table t1(id int(4) unsigned,name char(20));
验证1：有符号和无符号tinyint
有符号和无符号的tinyint验证2：int类型后面的存储是显示宽度，而不是存储宽度
int 后面存储是显示宽度1.2 浮点型
定点数类型: DEC等同于DECIMAL
作用：存储薪资、身高、体重、体质参数等
浮点类型：FLOAT DOUBLE
float 单精度 随着小数位数的增多,不准确
double 双精度 随着小数位数的增多.不准确,比float要准确
decimal 小数 精准的小数
语法 验证三种建表方式 验证三种类型的精度(3)日期类型
year 年份 (1901~2155)
date 年月日
time 时分秒
datetime 年月日 时分秒
now() sql语言中自带的内容函: 获取当前的时间(根据数据类型)
create table t10(born_year year,intClass datetime);
2.2 char类型 &varchar类型
#注意：char和varchar括号内的参数指的都是字符的长度
#char类型：定长，简单粗暴，浪费空间，存取速度快
字符长度范围：0-255（一个中文是一个字符，是utf8编码的3个字节）
存储：
存储char类型的值时，会往右填充空格来满足长度
例如：指定长度为10，存>10个字符则报错，存<10个字符则用空格填充直到凑够10个字符存储
检索：
在检索或者说查询时，查出的结果会自动删除尾部的空格，除非我们打开pad_char_to_full_length SQL模式（设置SQL模式：SET sql_mode = ‘PAD_CHAR_TO_FULL_LENGTH‘;
查询sql的默认模式：select @@sql_mode;）
#varchar类型：变长，精准，节省空间，存取速度慢
字符长度范围：0-65535（如果大于21845会提示用其他类型 。mysql行最大限制为65535字节，字符编码为utf-8：https://dev.mysql.com/doc/refman/5.7/en/column-count-limit.html）
存储：
varchar类型存储数据的真实内容，不会用空格填充，如果‘ab ‘,尾部的空格也会被存起来
强调：varchar类型会在真实数据前加1-2Bytes的前缀，该前缀用来表示真实数据的bytes字节数（1-2Bytes最大表示65535个数字，正好符合mysql对row的最大字节限制，即已经足够使用）
如果真实的数据<255bytes则需要1Bytes的前缀（1Bytes=8bit 2**8最大表示的数字为255）
如果真实的数据>255bytes则需要2Bytes的前缀（2Bytes=16bit 2**16最大表示的数字为65535）
检索：
尾部有空格会保存下来，在检索或者说查询时，也会正常显示包含空格在内的内容
小结
#常用字符串系列：char与varchar 注：虽然varchar使用起来较为灵活，但是从整个系统的性能角度来说，char数据类型的处理速度更快，有时甚至可以超出varchar处理速度的50%。因此，用户在设计数据库时应当综合考虑各方面的因素，以求达到最佳的平衡 #其他字符串系列（效率：char>varchar>text） TEXT系列 TINYTEXT TEXT MEDIUMTEXT LONGTEXT BLOB 系列 TINYBLOB BLOB MEDIUMBLOB LONGBLOB BINARY系列 BINARY VARBINARY text：text数据类型用于保存变长的大字符串，可以组多到65535 (2**16 − 1)个字符。 mediumtext：A TEXT column with a maximum length of 16,777,215 (2**24 − 1) characters. longtext：A TEXT column with a maximum length of 4,294,967,295 or 4GB (2**32 − 1) characters.
2.3枚举和集合
字段的值只能在给定范围中选择，如单选框，多选框
示例:
mysql> create table consumer(
-> id int,
-> name varchar(50),
-> sex enum(‘male‘,‘female‘,‘other‘) default ‘male‘,
-> level enum(‘vip1‘,‘vip2‘,‘vip3‘,‘vip4‘),#在指定范围内，多选一
-> fav set(‘play‘,‘music‘,‘read‘,‘study‘) #在指定范围内，多选多
-> );
Query OK, 0 rows affected (0.37 sec)
mysql> insert into consumer values(1,‘tony‘,‘male‘,‘vip2‘,‘play,study‘);
Query OK, 1 row affected (0.07 sec)
mysql> select * from consumer;
+------+------+------+-------+------------+
| id | name | sex | level | fav |
+------+------+------+-------+------------+
| 1 | tony | male | vip2 | play,study |
+------+------+------+-------+------------+
1 row in set (0.00 sec)
3.完整性约束
3.1 not null 与 default
如果单独设置not null 不能插入空值
如果即设置了not null,又指定default,可以插入空值,会走default
(1)默认值可以为空
mysql> create table t1(id int);# id字段默认可以为空 Query OK, 0 rows affected (0.05 sec) mysql> desc t1; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | id | int(11) | YES | | NULL | | +-------+---------+------+-----+---------+-------+ row in set (0.03 sec) mysql> insert into t1 values(); #给t1表插一个空的值 Query OK, 1 row affected (0.00 sec) #查询结果如下 mysql> select * from t1; +------+ | id | +------+ | NULL | +------+ row in set (0.00 sec) 默认值可以为空
(2)设置not null后 ,插入值不能为空
#给 num设置不能为空 mysql> create table t2(num int not null); Query OK, 0 rows affected (0.47 sec) mysql> desc t2; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | num | int(11) | NO | | NULL | | +-------+---------+------+-----+---------+-------+ 1 row in set (0.01 sec) #此时报错,显示不能插空值 mysql> insert into t2 values(); ERROR 1364 (HY000): Field ‘num‘ doesn‘t have a default value
(3) 如果即设置了not null,又指定default,可以插入空值,值为default,当插入值不是空值,结果是自己的值
#创建 t3表此时设置not null,并且default为 4 mysql> create table t3(num int not null default 4); Query OK, 0 rows affected (0.46 sec) mysql> desc t3; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | num | int(11) | NO | | 4 | | +-------+---------+------+-----+---------+-------+ 1 row in set (0.01 sec) #当插入数据为空时,此时是默认值生效 mysql> insert into t3 values(); Query OK, 1 row affected (0.11 sec) #但是也可以插入值但是此时却是给的值而不是默认值 mysql> insert into t3 values(2); Query OK, 1 row affected (0.11 sec) mysql> select * from db2.t3; +-----+ | num | +-----+ | 4 | | 2 | +-----+ 2 rows in set (0.00 sec)
3.2
(1)单列唯一
# 创建t4表,给name设置单列唯一 mysql> create table t4(id int not null,name char(20) unique); Query OK, 0 rows affected (0.47 sec) mysql> desc t4; +-------+----------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+----------+------+-----+---------+-------+ | id | int(11) | NO | | NULL | | | name | char(20) | YES | UNI | NULL | | +-------+----------+------+-----+---------+-------+ 2 rows in set (0.01 sec) mysql> insert into t4 values(1,‘alex‘); Query OK, 1 row affected (0.35 sec) mysql> insert into t4 values(1,‘alex‘); #有于给name设置了单列为一,因此插入相同的值会报错 ERROR 1062 (23000): Duplicate entry ‘alex‘ for key ‘name‘ #当将值改为与第一次不同时候,发现此时插入成功 mysql> insert into t4 values(1,‘alex2‘); Query OK, 1 row affected (0.34 sec) mysql> select * from db2.t4; +----+-------+ | id | name | +----+-------+ | 1 | alex | | 1 | alex2 | +----+-------+ 2 rows in set (0.00 sec)
两种书写方式:
create table t4(
id int not null,
name char(20) unique
);
create table t4(
id int not null,
name char(20),
unique(name)
);
insert into t4(id,name) values(1,‘alex‘);
insert into t4(id,name) values(1,‘wusir‘);
(2)多列唯一:只要有一列是相同的就不能插入.
#书写
create table t5( id int, name char(20), unique(id), unique(name) );
#创建文件t5 ,此时将id 和name都设置 unique
mysql> create table t5(
-> id int,
-> name char(20),
-> unique(id),
-> unique(name)
-> );
Query OK, 0 rows affected (0.58 sec)
#插入一组值
mysql> insert into t5 values(2,‘alex‘);
ERROR 1062 (23000): Duplicate entry ‘alex‘ for key ‘name‘
#插入有相同内容的值时候报错
mysql> insert into t5 values(1,‘alex2‘);
ERROR 1062 (23000): Duplicate entry ‘1‘ for key ‘id‘
#当所有内容都不同时才能插入
mysql> insert into t5 values(2,‘alex2‘);
Query OK, 1 row affected (0.10 sec)
mysql> desc t5;
+-------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id | int(11) | YES | UNI | NULL | |
| name | char(20) | YES | UNI | NULL | |
+-------+----------+------+-----+---------+-------+
2 rows in set (0.01 sec)
mysql> select * from db2.t5;
+------+-------+
| id | name |
+------+-------+
| 1 | alex |
| 2 | alex2 |
+------+-------+
2 rows in set (0.00 sec)
(3)联合唯一:多列相同时不能插入
**适用场景 学生选课
#书写
create table t6(
id int,
name char(20),
unique(id,name)
);
#创建t6表 ,设置联合唯一
mysql> create table t6(
-> id int,
-> name char(20),
-> unique(id,name)
-> );
Query OK, 0 rows affected (0.47 sec)
mysql> desc t6;
+-------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id | int(11) | YES | MUL | NULL | |
| name | char(20) | YES | | NULL | |
+-------+----------+------+-----+---------+-------+
2 rows in set (0.01 sec)
mysql> insert into t6 values(1,"alex");
Query OK, 1 row affected (0.35 sec)
#当插入相同的两列记录会报错
mysql> insert into t6 values(1,"alex");
ERROR 1062 (23000): Duplicate entry ‘1-alex‘ for key ‘id‘
mysql> insert into t6 values(2,"alex");
Query OK, 1 row affected (0.11 sec)
#但是当两列记录中的一项内容不同就可以插入
mysql> insert into t6 values(1,"wusir");
Query OK, 1 row affected (0.10 sec)
mysql> select *from t6;
+------+-------+
| id | name |
+------+-------+
| 1 | alex |
| 1 | wusir |
| 2 | alex |
+------+-------+
3 rows in set (0.01 sec)
3.3 主键primary key (not null + unique 的结果)
(1)单列主键 不能为空 ,并且是唯一
#书写
# primary key 索引(针对于大量数据) 查询速度要快
create table t7(
id int primary key,
name varchar(10) unique
);
#相同结果的写法
create table t8(
id int not null unique,
name varchar(10) unique
);
#创建t7表 此时为id设置主键,并且 name唯一
mysql> create table t7(
-> id int primary key,
-> name varchar(10) unique
-> );
Query OK, 0 rows affected (0.51 sec)
mysql> desc t7;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | NO | PRI | NULL | |
| name | varchar(10) | YES | UNI | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.01 sec)
#当插入空值时候回报错
mysql> insert into t7 values();
ERROR 1364 (HY000): Field ‘id‘ doesn‘t have a default value
mysql> insert into t7(id,name) values(1,"wusir");
Query OK, 1 row affected (0.37 sec)
#id唯一且不能为空
mysql> insert into t7(id,name) values(1,"wusir");
ERROR 1062 (23000): Duplicate entry ‘1‘ for key ‘PRIMARY‘
mysql> insert into t7(id,name) values(1,"wusir2");
ERROR 1062 (23000): Duplicate entry ‘1‘ for key ‘PRIMARY‘
mysql> insert into t7(id,name) values(2,"wusir2");
Query OK, 1 row affected (0.35 sec)
mysql> select *from db2.t7;
+----+--------+
| id | name |
+----+--------+
| 1 | wusir |
| 2 | wusir2 |
+----+--------+
2 rows in set (0.00 sec)
(2)联合主键
#书写方式
create table t9(
id int,
name varchar(10),
primary key(id,name)
);
#创建了t9表,此时可以设置空值
mysql> create table t9(
-> id int,
-> name varchar(10),
-> primary key(id,name)
-> );
Query OK, 0 rows affected (0.30 sec)
mysql> desc t9;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | NO | PRI | 0 | |
| name | varchar(10) | NO | PRI | | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.01 sec)
mysql> insert into t9 values();
Query OK, 1 row affected (0.11 sec)
mysql> insert into t9(id name) values(1,"alex");
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘name) values(1,"alex")‘ at line 1
mysql> insert into t9(id, name) values(1,"alex");
Query OK, 1 row affected (0.10 sec)
mysql> insert into t9(id, name) values(1,"alex2");
Query OK, 1 row affected (0.11 sec)
mysql> select *from db2.t9;
+----+-------+
| id | name |
+----+-------+
| 0 | |
| 1 | alex |
| 1 | alex2 |
+----+-------+
3 rows in set (0.00 sec)
**学生选课可以为空
3.4.auto_increment (自增长)
#书写方式
create table student(
id int primary key auto_increment,
name varchar(20) not null,
sex enum(‘male‘,‘female‘) default ‘male‘,
ip varchar(20) unique
);
insert into student(name,sex,ip) values (‘alex‘,‘female‘,‘127.0.0.5‘),(‘wusir‘,‘male‘,‘173.45.32.1‘);
mysql> create table student(
-> id int primary key auto_increment,
-> name varchar(20) not null,
-> sex enum(‘male‘,‘female‘) default ‘male‘,
-> ip varchar(20) unique
-> );
Query OK, 0 rows affected (0.23 sec)
mysql> insert into student(name,sex,ip) values (‘alex‘,‘female‘,‘127.0.0.5‘),(‘wusir‘,‘male‘,‘173.45.32.1‘);
Query OK, 2 rows affected (0.37 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> desc student;
+-------+-----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(20) | NO | | NULL | |
| sex | enum(‘male‘,‘female‘) | YES | | male | |
| ip | varchar(20) | YES | UNI | NULL | |
+-------+-----------------------+------+-----+---------+----------------+
4 rows in set (0.01 sec)
mysql> select *from student;
+----+-------+--------+-------------+
| id | name | sex | ip |
+----+-------+--------+-------------+
| 1 | alex | female | 127.0.0.5 |
| 2 | wusir | male | 173.45.32.1 |
+----+-------+--------+-------------+
2 rows in set (0.00 sec)
涉及到删除时:
#当删除第二条记录时候,会发现此时的结果任然保留id为2 时的序号 mysql> delete from student where id =2; Query OK, 1 row affected (0.49 sec) mysql> select *from student; +----+-------+--------+------------+ | id | name | sex | ip | +----+-------+--------+------------+ | 1 | alex | female | 127.0.0.5 | | 3 | alex1 | male | 127.1.0.12 | +----+-------+--------+------------+ 2 rows in set (0.00 sec) #在插入记录时候,会在后续排列 mysql> insert into student(name,sex,ip) values (‘alex3‘,‘male‘,‘127.1.5.72‘); Query OK, 1 row affected (0.11 sec) mysql> select *from student; +----+-------+--------+------------+ | id | name | sex | ip | +----+-------+--------+------------+ | 1 | alex | female | 127.0.0.5 | | 3 | alex1 | male | 127.1.0.12 | | 4 | alex3 | male | 127.1.5.72 | +----+-------+--------+------------+ 3 rows in set (0.00 sec) #但是可以指定id进行插入 mysql> insert into student(id,name,sex,ip) values (2,‘wusir‘,‘male‘,‘127.3.5.9‘); Query OK, 1 row affected (0.11 sec) mysql> mysql> Ctrl-C -- exit! select *from student; +----+-------+--------+------------+ | id | name | sex | ip | +----+-------+--------+------------+ | 1 | alex | female | 127.0.0.5 | | 2 | wusir | male | 127.3.5.9 | | 3 | alex1 | male | 127.1.0.12 | | 4 | alex3 | male | 127.1.5.72 | +----+-------+--------+------------+ 4 rows in set (0.00 sec) #清空记录 mysql> delete from student; Query OK, 4 rows affected (0.36 sec) mysql> delete from student; Query OK, 0 rows affected (0.00 sec) mysql> show tables; +---------------+ | Tables_in_db2 | +---------------+ | student | | t1 | | t2 | | t3 | | t4 | | t5 | | t6 | | t7 | | t9 | +---------------+ 9 rows in set (0.11 sec) #但是会保留自增长的序号,后续插入 mysql> insert into student(name,sex,ip) values (‘alex3‘,‘male‘,‘127.1.5.72‘); Query OK, 1 row affected (0.36 sec) mysql> select *from student; +----+-------+------+------------+ | id | name | sex | ip | +----+-------+------+------------+ | 5 | alex3 | male | 127.1.5.72 | +----+-------+------+------------+ 1 row in set (0.00 sec) #但是使用truncate时候,不会保留增长的序号 mysql> truncate table student; Query OK, 0 rows affected (0.21 sec) mysql> show tables; +---------------+ | Tables_in_db2 | +---------------+ | student | | t1 | | t2 | | t3 | | t4 | | t5 | | t6 | | t7 | | t9 | +---------------+ 9 rows in set (0.00 sec) mysql> select *from student; Empty set (0.00 sec) mysql> insert into student(name,sex,ip) values (‘alex3‘,‘male‘,‘127.1.5.72‘); Query OK, 1 row affected (0.35 sec) #再次插入时候从一开始 mysql> select *from student; +----+-------+------+------------+ | id | name | sex | ip | +----+-------+------+------------+ | 1 | alex3 | male | 127.1.5.72 | +----+-------+------+------------+ 1 row in set (0.00 sec)
delete from t1; #如果有自增id，新增的数据，仍然是以删除前的最后一样作为起始。
truncate table t1;数据量大，删除速度比上一条快，且直接从零开始。
3.5
# 先创建主表
mysql> create table dep(
-> id int primary key auto_increment,
-> name char(10) unique,
-> dep_desc varchar(50) not null
-> );
Query OK, 0 rows affected (0.47 sec)
#创建从表
mysql> create table emp(
-> eid int primary key auto_increment,
-> name char(10) not null,
-> age int not null,
-> dep_id int,
-> school_id int,
-> constraint fk_dep foreign key(dep_id) references dep(id) );
Query OK, 0 rows affected (0.55 sec)
#主表插入数据
mysql> insert into dep(name,dep_desc) values(‘校长部‘,‘校长管理有限部门‘),(‘公关部‘,‘公关管理有限部门‘),(‘IT部门‘,‘IT技 术有限部门‘),(‘财务部‘,‘管钱很多部门‘);
Query OK, 4 rows affected (0.11 sec)
Records: 4 Duplicates: 0 Warnings: 0
#从表插入数据
mysql> insert into emp(name,age,dep_id)
-> values
-> (‘alex‘,18,1),
-> (‘wusir‘,30,2),
-> (‘吴老板‘,20,3),
-> (‘马老板‘,18,4),
-> (‘邱老板‘,20,2),
-> (‘女神‘,16,3);
Query OK, 6 rows affected (0.06 sec)
Records: 6 Duplicates: 0 Warnings: 0
#将从表中对应主表的id为2 的项删除
mysql> delete from emp where dep_id =2;
Query OK, 2 rows affected (0.37 sec)
mysql> select *from emp;
+-----+-----------+-----+--------+-----------+
| eid | name | age | dep_id | school_id |
+-----+-----------+-----+--------+-----------+
| 1 | alex | 18 | 1 | NULL |
| 3 | 吴老板 | 20 | 3 | NULL |
| 4 | 马老板 | 18 | 4 | NULL |
| 6 | 女神 | 16 | 3 | NULL |
+-----+-----------+-----+--------+-----------+
4 rows in set (0.00 sec)
#此时可以将主表中id为2的部门删除
mysql> delete from dep where id=2;
Query OK, 1 row affected (0.35 sec)
mysql> select *from dep;
+----+-----------+--------------------------+
| id | name | dep_desc |
+----+-----------+--------------------------+
| 1 | 校长部 | 校长管理有限部门 |
| 3 | IT部门 | IT技术有限部门 |
| 4 | 财务部 | 管钱很多部门 |
+----+-----------+--------------------------+
3 rows in set (0.00 sec)
#但是若果直接删除,会报错,因为此时该id对应的存在内容
mysql> delete from dep where id=3;
ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails (`db2`.`emp`, CONSTRAINT `fk_dep` FOREIGN KEY (`dep_id`) REFERENCES `dep` (`id`))
所以要同步删除和同步更新
#当在创建从表时添加 on delete cascade on update cascade 同步更新同步删除 mysql> select *from dep; +----+-----------+--------------------------+ | id | name | dep_desc | +----+-----------+--------------------------+ | 1 | 校长部 | 校长管理有限部门 | | 2 | 公关部 | 公关管理有限部门 | | 3 | IT部门 | IT技术有限部门 | | 4 | 财务部 | 管钱很多部门 | +----+-----------+--------------------------+ 4 rows in set (0.00 sec) #直接删除部门可以,而对应的部门内的人也删除 mysql> delete from dep where id=2; Query OK, 1 row affected (0.35 sec) mysql> select *from dep; +----+-----------+--------------------------+ | id | name | dep_desc | +----+-----------+--------------------------+ | 1 | 校长部 | 校长管理有限部门 | | 3 | IT部门 | IT技术有限部门 | | 4 | 财务部 | 管钱很多部门 | +----+-----------+--------------------------+ 3 rows in set (0.00 sec) mysql> select *from emp; +-----+-----------+-----+--------+-----------+ | eid | name | age | dep_id | school_id | +-----+-----------+-----+--------+-----------+ | 1 | alex | 18 | 1 | NULL | | 3 | 吴老板 | 20 | 3 | NULL | | 4 | 马老板 | 18 | 4 | NULL | | 6 | 女神 | 16 | 3 | NULL | +-----+-----------+-----+--------+-----------+ 4 rows in set (0.00 sec)
标签：sig 数值 roo 空格 strong ica 多选 指定 def
原文地址：https://www.cnblogs.com/wcx666/p/10554917.html
